Contemporary hard disk drivers (HDD) typically include a brushless DC motor within which a disk rotating spindle assembly for rotating at least one data storage disk at a desirable velocity, typically in a range between 5,000 and 10,000 revolutions per minute, is provided. Storage disk devices such as a magnetic disk devices etc. have been widely utilised as a storage devices of a computer etc.
Hard disk drivers also typically include a rotary actuator structure powered by a Voice Coil Motor (VCM). The rotary actuator structure positions one or more transducer heads at desired locations relative to surfaces of the disk or disks. More precisely the VCM moves the head radially over the disk surface to thereby enables the head to be positioned over any annular track on the surface. In normal operation, the VCM, in response to control signals coming from the computer, positions the transducer head radially for recording data signals on or retrieving data signals from a pre-selected one of a set of concentric recording tracks on the disk.
The transducer head is supported above the disk surface by a film of air to prevent contact therebetween which might thereby otherwise damage one or both members. The head is typically designed to actually fly above the disk recording surface of height less than 50 microinches.
When the HDD is in power down condition the transducer head must be placed on a parking zone to avoid any mechanical damages determined by the contact between the head and the disk surface. The parking zone may find on the central part of the disk surface or outside the disk.
The placing of the head on the parking zone occurs even in emergency condition, that is in condition of high temperature or in presence of sudden knocks or when an electrical power failure slows the disk, which allows the head to settle into contact with the disk surface.
Generally all the modern disk drives incorporate means for moving the head on the parking zone; this means is even activated when the disk speed does not remain within tolerances, when a positional error is detected or when write circuits faults that could affect the stored data are detected.
A means for moving the head on the parking zone is disclosed in U.S. Pat. No. 6,188,192 wherein a disk drive system is described which includes a disk having a magnetic surface and supported for rotation on a spindle, a magnetic head being movable relative to the magnetic surface, and a spindle motor for driving the spindle. The motor generates a back electromotive force voltage, so called BEMF voltage, during an emergency condition and the system comprises a plurality of switches for switching said BEMF voltage and a plurality of comparators for comparing each phase of the BEMF voltage. The system comprises a control circuit adapted to control the plurality of switches to supply said BEMF voltage; the control circuit comprises a decoder and a latch and provides to rectify said BEMF voltage: This rectified BEMF voltage is supplied to the VCM which directs said head to a stored position.
The above mentioned disk drive system however is complex and presents high cost for its fabrication due above all to the use of at least three comparators one for each phase of the BEMF voltage.